The proposed research will trace the evolution of bloodfeeding (hematophagy) in the Simuliidae (black flies) in relation to host selection and will also analyze the chemical composition of saliva in relation to its possible contribution to successful transmission of Onchocerca volvulus, a major human filarial parasite. In particular, we will focus on the interaction and evolution of a powerful anticoagulant (I Oa or prothrombinase complex inhibitor) which was recently described from Simulium vittatum with apyrase, a ubiquitous and important anti-platelet aggregation factor (enzyme) which occurs in variable amounts in Simulium spp. We will also determine the presence of specific salivary secretions that permit successful bloodfeeding while possibly aiding in the transmission of Onchocerca spp. parasites. This will include comparing levels of salivary gland histamine in both anthropophilic and zoophilic Simulium spp. as well as searching for an erythema inducing factor in the anthropophilic species if histamine levels should be unusually lower than those in the zoophilic counterparts. We will also identify both immunogenic and immunosuppressive antigens present in black fly saliva. Immunosuppressive antigens will be recognized by plaque forming assay and immunogenic antigens by cell proliferation assay and by quantifying antibodies to sheep red blood cells and to black fly saliva. In order to pinpoint such antigens, saliva will be fractioned according to high and low molecular weight fractions and experiments will be carried out in similar fashion. Finally, in order to more clearly identify possible immunosuppressive effects of black fly saliva on filarial (Onchocerca spp.) transmission, similar studies will also be conducted with O. lienalis L33 antigen as a substitute for the sheep red blood cells. Very little is known about the role of saliva in the bloodfeeding physiology of Simulium spp., particularly in comparison with other major arthropod disease vectors. Findings from this study should provide a useful frame of reference for comparison, as well as a first step in understanding the evolution of Onchocerca spp. vectors in the Simuliidae and Ceratopogonidae.